The Life Cycle of HIV

HIV and AIDS

HIV and AIDS

HIV (human
immunodeficiency virus) is a virus that in time can lead to AIDS (acquired
immunodeficiency syndrome). HIV attacks and weakens the immune system,
specifically the immune cells that are called CD4 cells or T-cells. Unlike many
other viral infections, our bodies are unable to eliminate HIV completely.

Eventually,
when the virus has destroyed so many CD4 cells that the immune system is
largely non-functional, the damage leads to AIDS, the most advanced stage of
HIV. A person with AIDS is susceptible to any number of infections due to one’s
damaged immune system.

Transmission of HIV

Transmission of HIV

The Centers for Disease
Control and Prevention (CDC) reports that in the United States,
HIV is largely transmitted from one person to another through unprotected sex
and through shared drug needles. While rare, the virus can also be transmitted
though a blood transfusion.

Infection occurs in parts of the body that are lined with
a mucus membrane. Here, the virus attaches to immune cells, which are then
transported to the lymph nodes. From the lymph nodes, the virus can begin to
infect CD4 cells, the cells that coordinate the body’s immune response.

The HIV Life Cycle Begins with Attachment

The HIV Life Cycle Begins with Attachment

Scientists have yet to determine why the human immune
system cannot get rid of HIV. To better understand the virus and develop
treatments, researchers have worked toward determining the virus’s life cycle
in the body.

The first stage is attachment, or binding. This is when
the virus finds and attaches to the outside of a CD4 cell. HIV finds and binds
to CD4 cells via a receptor. The virus functions like a key that fits into a
specific lock, or receptor, on the outside of the immune cell.

The Virus Enters the Host Cell

The Virus Enters the Host Cell

Once HIV has found and attached to a receptor on a CD4 cell,
it has to enter the cell in order to infect it and replicate itself. This stage
is called fusion. The outer wall of the virus, called the envelope, fuses with
the membrane of the CD4 cell. This fusion allows the virus to get inside of the
immune cell with its genetic material.

Reverse Transcription: Genetic Conversion

Reverse Transcription: Genetic Conversion

Within the cells of the human body, our genetic material
is in the form of a molecule called deoxyribonucleic acid, or DNA. HIV’s
genetic material is the form of ribonucleic acid (RNA) instead of DNA.

To take over a human immune cell, the virus has to
convert its RNA to DNA. This process occurs using an enzyme called reverse
transcriptase. The virus releases this enzyme once it has entered the CD4 cell
so it can begin the conversion process, called reverse transcription.

Integration: Taking Over the DNA

Integration: Taking Over the DNA

Once reverse transcription is complete and the virus has
its genetic material in the form of DNA, it can enter the CD4 cell’s nucleus.
This is where the cell keeps its DNA. Inside the nucleus, the virus joins its
DNA to the cell’s DNA. In other words, it integrates its genetic material into
that of the host cell. The HIV uses an enzyme called integrase to do this.

Transcription and Translation: Building HIV Proteins

Transcription and Translation: Building HIV Proteins

Once the virus has integrated its DNA into that of the
host cell, it can hijack its machinery and begin to manufacture copies of its
own genetic material and its own proteins. The virus uses the enzymes and other
structures inside the CD4 cell to replicate itself.

Assembly and Budding: The Infection Progresses

Assembly and Budding: The Infection Progresses

With all the parts needed to make more viruses, thanks to
the machinery of the CD4 cell, copies of the virus begin to assemble inside the
cell. The viruses are simple, and need only their copied RNA and some proteins
to assemble into new viral packages.

Once they are fully put together, the new viruses leave
the CD4 cell through a process called budding. The viruses push against the
membrane of the CD4 cell to get out and take part of the membrane with them to
create their own envelopes. These new viruses can now infect other CD4 cells
and repeat the life cycle all over again.

Treatments Target Stages of the HIV Life Cycle

Treatments Target Stages of the HIV Life Cycle

Through understanding the life cycle of HIV, researchers
have developed treatments that target the virus. While there is no cure, the
drugs have been successful in keeping patients with HIV healthy for many years.

Some drugs target the receptors on CD4 cells, preventing
HIV from binding to them. Others inhibit reverse transcriptase to prevent the
virus from converting its RNA into DNA. And some medications prevent the enzyme
integrase from allowing HIV to get into the CD4 cell nucleus.

There are many different ways you can contract HIV: through unprotected sex, by sharing needles, and, more rarely, via a blood transfusion. Your chances of contracting HIV vary depending on several factors.

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